Basic bricks offer is higher thermal conductivity, around 3 W/mK in com-parison to Alumina which has thermal conductivity of 2 W/mK or thereabouts. Burner flame temperatures at the tip vary between 2000°C and 2200°C, depending on the type of fuel being used. For some reason, if the burner flame touches the re-fractory lining, an Alumina lining cannot dissipate heat fast enough and will melt. Basic bricks on the other hand can not only withstand higher temperatures if exposed to flame, but can pass on the heat at a fast-er rate towards the kiln surface too. There-by reducing flame-related failure rates.Basic bricks also generally give better life

The India Advantage Basically

Severe Coating ConditionsWhen does a desirable coating become undesirable, and how does one prevent such situations

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Basics of BasicCriticality of operating conditions some-times force cement manufacturers to opt for Basic bricks to avoid unplanned and unwanted stoppages. E.g. if ther-mal load in the kiln is higher than 5.5 GCal/m2 and the kiln is being fired with high amount of petcoke or alternative fuel, it is safer to use a Basic brick lining. Basic bricks offer a clear advantage over Alumina brick linings: while good quality Alumina bricks can withstand temperatures of up to 1600°C, good quality Basic bricks can extend this tol-erance up to 1750°C. Another advantage

than Alumina bricks under higher ther-mal load and continuous operation of the kiln. For larger kilns, producing more than 6000 TPD, a Basic brick lining often promises a more economical lining option since it eliminates unforeseen shutdowns. It should be reiterated here that Basic bricks offer good performance under con-tinuous operation only. For intermittent operations, they deteriorate faster than Alumina due to their higher expansion and contraction on every startup and shutdown.

Current ScenarioFor top-quality, high-performance Basic re-fractory bricks for kilns, manufacturers have

no option but to turn to imports. Aside from foreign currency related challenges, plants have to maintain unusually high inventories to protect against unforeseen delays or dis-ruptions in the midst of long delivery cycles. Another challenge is the perishable na-ture of these bricks, with shelf-lives of about one year. So if the plant is in a hu-mid area, the bricks hydrate and are un-usable at the time of lining. Moreover in case of urgent requirements, imported bricks are not available at short notice.In a nutshell, reliance on imports means higher-than-necessary investments and poor cost-benefit scenarios.

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Cement manufacturers are increasingly opting for Basic refractory bricks because of the clear advantages they offer. The new & improved Magnel 85 takes it even further.

January 2019 For private circulation onlyA quarterly by Cement Refractory BU of Dalmia-OCL

Severe Coating Conditions & Remedies Thereof

Type 2At the beginning of burning zone, coat-

ings or rings are formed by sintered material. Here all the CO2 has been driven out of Calcium Carbonate and the liberat-ed lime has begun to combine with acidic SiO2, Al2O3 and Fe2O3. Coating begins to form as soon as the temperature is high enough for significant flux formation. And any local cooling can cause this flux to freeze turning good coating into bad. Flux softens when exposed to kiln at-mosphere and stiffens when it turns into the charge. Solid particles from charge stick into flux and a ring might form.

Rings so formed have a tendency to grow rapidly and are usually tackled by adjust-ments to the main burner. Slight shift in temperatures affects the point where flux is first formed, and very often the rings break to form at a different point.

Type 4When secondary combustion air drawn

into the kiln leads to cooling of the clinker falling over the nose ring, it some-times causes stiffening of flux in the clinker and its adhesion to the refractory lining. This tends to dam the combined clinker in the kiln at high temperatures and might lead to clinker quality problems. A common solution for such outlet rings is to push the burner into the kiln creating a clinker cooling zone within the kiln itself.

More problematic are longer middle rings caused by recirculation of clin-

ker dust from cooler through secondary air. Dusty clinker leads to heavy dust bur-den on secondary air drawn into kiln from the cooler. The flux in clinker particles re-melts and due to burner momentum, clin-ker droplets get carried back towards inlet, up to a point where the flux stiffens again and sticks to the refractory lining. An elon-gated ring builds up in layers with a fine structure showing curvature of the kiln. The solution here is to eliminate recircu-lating dust from the cooler which is gen-erally triggered by long, lazy flames that lead to higher sulphate recirculation with slow heating and cooling of the clinker.

Type 3

It is a well-known fact that coatings in ce-ment kilns protect refractory linings from

thermal shocks, abrasion by kiln charge and chemical infiltration of gases. The uneven surface of a coating assists in transfer of heat to the kiln charge by causing the charge to climb-and-tumble as the kiln rotates. Coatings also thicken the effective refrac-tory lining of the kiln, increases insulation of the kiln shell from high process tem-peratures and reduces radiation losses and thus overall thermal energy consumption.

Formation of a ‘good’ coating depends on the kiln feed, clinker properties, refractory lining material and operating conditions of the kiln.

Increasing the Alumina to Iron ratio restricts coating build-up. A similar effect is ob-served when Silica to Iron ratio is increased.

A stable operation is critical for main-taining stable coating in the kiln. Any changes in kiln feed or combustion of fuel in the main burner affect the tem-perature profile, amount and properties of the flux in different areas of the kiln.

Coatings Are Desirable

The Tipping PointWhen coating grows beyond a thick-

ness of half a meter, becomes a ring, it poses a problem. It suddenly becomes undesirable! And this happens when the accretion tendency of the coating out-weighs its erosion tendency. Before we get into the reasons as to why such a phe-nomenon occurs, let’s look at what are the different types of undesirable coatings that form in different parts of the kiln.

The most common type of coating is Sulphate spurrite 2C2SCaSO4, its

most common cause being the pres-ence of sulphur in petcoke. These rings create a sort of dam that impedes free flow of material from the inlet. Which is problematic as they are too far in from the outlet in the calcining zone. The only way to deal with these formations is to use refractories containing Silicon Carbide, since they help create a glass-like surface of Silica that disallows coating formation. Sulphate spurrite rings are either unable to form or get dislodged very easily due to movement of the kiln and abrasion with charge.

Type 1

Bottom Left: SEM photo showing plate-like crys-tals of sulphospurriteBottom right: C2S (1), C4AF (2), CaO (3), K2SO4*2Ca-SO4 (4), 2C2S*CaSO4 (5)

Dalmia Seven was asked to submit a recommendation for smoke chamber area, bearing the following operating conditions in mind:

1. Coating formation2. High temperatures3. Chemical attacks from alkalies4. High abrasion

Dalmia Seven’s technical team con-cluded that the ideal recommendation would have to ensure properties and features such as:

• Low Cement castable with Silicon Carbide content

• Main raw material: Adalusite + SiC

+ some selected additive• Al2O3 - 37.4%, SiC - 30.7%• Good thermal shock resistance• Good alkali resistance• Good mechanical abrasion resis-

tance• CCS 1000 kg/cm2 at 800°C - 1200°C• Good coating repellent properties

Dalmia Seven’s DS CAST 30 NC SIC was therefore recommended. A trial installation in the smoke chamber area of 5 MT of castable was carried out in Kiln #1 in Nov 2018. Water require-ment was approx. 4.5%. Just 2 days after installation, the kiln was lit up. Dalmia Seven & ACC Kymore teams are jointly monitoring performance of the installed castable and are awaiting any upcoming shutdown for inspection.

RECENT INSTALLATIONS

Challenge

Solution

Dalmia Seven was asked to submit a recommendation for burner pipe, bear-ing the following operating conditions in mind:

1. High temperatures2. High thermal shocks3. High chemical attacks4. High abrasion due to clinker dust

Dalmia Seven’s technical team con-cluded that the ideal recommendation would have to ensure properties and features such as:

• Andalusite-based low cement castable with Silicon Carbide

• Main raw material: Andalusite

(Al2O3 51%) + SiC (9.6%) + special additive

• Good thermal shock resistance / good thermal stability at all tem-peratures

• Good alkali resistance• Good mechanical abrasion resis-

tance• CCS 1050 kg/cm2 at 800°C - 1200°C

Dalmia Seven’s DS CAST 50 RD 01 W was recommended. A trial installation in the burner pipe of 5 MT of castable was carried out. Water requirement was approx. 4.5%. The burner pipe was put into operation in Dec 2018. Dalmia Seven & DCBL Ariyalur teams are jointly monitoring performance of the installed castable and are awaiting any upcoming shutdown for inspection.

Challenge

Solution

DS CAST 30 NC SIC ACC - Kymore Cement Works

DS CAST 50 RD 01 W Dalmia Cement (Bharat) - Ariyalur Cement Works

Now Reduce Your Fuel Costs With The All-New Alite

While Type 2, 3 & 4 type of rings can be tackled with process alone, for Type 1 rings, the only solution is to use specialised refractory bricks containing Silicon Carbide (SiC). Dal-

mia-OCL’s specially developed DAL-CR range of bricks containing SiC offer very high Alkali and Sulphur resistance with anti-coating properties that inhibit ring formation. Used in all kinds of kilns, fired with or without alternate fuels, these bricks are a proven option with long service life.

DAL-CR to the rescue

ALITE is a high-strength Low-Alumina energy-saving brick which not only withstands abrasion from kiln feed for a longer campaign life, but also reduces thermal en-ergy losses. Specially developed for calcination & inlet zones (0-15 M), ALITE has excellent Alkali and Sulphur resistance properties. Compared to denser 40% Al2O3 bricks, ALITE is nearly 45% more effective in controlling radiation losses. The best part is, with fuel cost savings it pays back for itself in under 3 months.

It is important that the Basic brick matrix has Silica and Lime in proper proportions so that refractoriness of the matrix is well above clinkerisation temperature. Keep-ing Silica and Lime in 1:2 or higher proportions helps in formation of DiCalcium Silicate (C2S) or TriCalcium Silicate (C3S) in brick structure. DiCalcium or TriCalcium Silicates can withstand temperatures above 2000°C giv-ing bricks the ability to easily withstand clinkerisation temperatures ranging from 1280°C to 1350°C without any softening of the matrix.

When Silica and Lime are in almost equal proportions, there are possibilities of formation of low temperature melting phases like MontiCellite, Merwinite etc. These phases start melting near clinkerisation temperature. Brick matrix therefore becomes soft and performance of brick is adversely affected.

Advantage of maintaining the CaO/SiO2 ratio in the Basic brick matrix at 2:1 ratio or higher

How do you like The Refractory Beat? Bouquets, brickbats, suggestions & feedback - email us all at Comms@DalmiaOCL.com. We’d love to hear from you.

The India Advantage ExplainedMade from imported raw material at Dal-mia-OCL’s state-of-the-art manufactur-ing facility in Rajgangpur, Odisha, Magnel 85 is at par with the best in the world in terms of quality, finish and performance. Importantly, Magnel 85 finally gives In-dian cement producers a better option. They can now choose to lower and un-lock their investments, pay in local cur-rency, manage inventories smartly thanks to incredibly shorter delivery cycles. And last but not the least, get faster service support in view of the geographical con-venience. That’s the India advantage.

Evolution of Magnel 85Cement manufacturing is a ‘basic’ pro-cess due to presence of lime. Refracto-ries need to be ‘basic’ therefore to with-stand clinker corrosion. Of all commonly used refractory materials, MgO has so far been the obvious choice for manu-

facturing basic bricks since they offer maximum resistance to cement clinker corrosion. There’s one problem though.MgO behaves poorly when it comes to thermal shock resistance. An MgO lining will crumble and fall down in its entirety as soon as the cement kiln is stopped and cooled. To address this, some other mate-rial has to be mixed with MgO grains, to act as a modifier and to impart thermal shock resistance to refractory. Advanced basic bricks are thus made up of two com-ponents: one is resistor which provides resistance against thermochemical attacks by cement clinker, and the other is modi-fier which helps increase resistance to thermal shocks. Not only that, the modifier also provides greater structural flexibility. It creates a crack-network inside the brick’s microstructure for fracture toughness, which is essential to cope with mechanical stresses coming from thermal expansion, kiln shell ovality and shell deformation.

Magnel 85 DevelopmentFor the new and improved Magnel 85, Dal-mia-OCL put greater emphasis on mod-ifier since this is the component which is put to test as soon as the kiln is fired. It is also vulnerable to clinker corrosion than MgO grains which are resistant to clinker corrosion. It is possible that the modifier will react with cement clinker at higher temperatures to form low melting secondary Calcium-Alumina compounds which will increase brick density to make the lining lose its elasticity and result in wear. Keeping this in mind, Magnel 85 uses Zirconia compounds in modifier as these form compounds with high refractoriness with cement clinker. Therefore bricks can be used in thermally highly loaded tran-sition zones to achieve a satisfactory life.

Since fused Spinel reduces wear rate of kiln linings considerably, Magnel 85 em-ploys synthetic Magnesia with a higher

primary crystal size, along with fused Spi-nel or modifier with Zirconia additives. In Magnel 85, it has also been ensured that Fe2O3 content is <1% so that volume change due to redox reaction is nominal and bricks are resistant to redox attacks.

Magnel 85, the Super BrickWhile on one hand, due to its high hot strength, Magnel 85 bricks with addition of Zirconia can be used under severe thermal and thermochemical loads, this also makes them suitable for different parts of the kiln.

Magnel 85 is characterised by high abra-sion and thermal shock resistance mak-ing it suitable for outlet and lower tran-sition zones where main stresses come from lining thrust on retainer, abrasion from cement clinker, thermal load due to burner flame and thermal shock.

In central burning zone, bricks are mostly covered by a stable coating. Bricks are there-fore expected to be coating-friendly. Magnel 85 has optimum levels of coatability making them suitable for central burning zone also.

Stresses in upper transition zone come from thermal shocks due to rapidly chang-ing coating conditions, thermochemical attacks from alkali and Sulphur, and clin-ker melt infiltration. This is also the area where the second tyre is located which causes mechanical loads in case of oval-ity. Excellent thermomechanical and thermochemical properties of Magnel 85 make them suitable for this area too.

Magnel 85, the Super Brick, is suitable for all basic zones in a cement kiln. With its unique combination of synthetic Magnesia, fused Spinel, Zirconia additives to match different types of loads in different parts of the cement kiln, it is just the solution Indian manufacturers need to take care of severe operating conditions at best pos-sible value. The best part, it is made right here in your neighbourhood. Made in India.

Continued from first page

Predominant Wear Mechanisms in Rotary Kilns

Magnel 85 Recent Performance Data

Q1. What advantage do Basic bricks offer over Alumina bricks?

a) Ability to withstand higher temperatures

b) Higher thermal conductivity c) BothQ2. Special refractory bricks contain-

ing SiC can be used to address all types of severe coating condition

a) True b) False

Find out by simply answering a couple of questions. And should you want, email your answers to Comms@DalmiaOCL.com for a FREE Beat t-shirt! But hurry, only 20 t-shirts are up for grabs and will be given away on first-come-first-served basis to those who get their answers right. Here goes…

Did you catch the beat?Plant/Works Kiln Diameter Production (TPD)

Basic Lining Length Life

JAYPEE ANDHRA 4.35 4500 X 1 Year

JK GOTAN 3.6 3000 0.0-6.0 1 Year

CALCOM CEMENT, UMRANGSU (RUNNING) 3.8 3400 2.0-16.0 1 Year

OCL RAJGANGPUR LINE 1 (RUNNING) 3.8 3000 0.8-2.6 &

24.0-26.0 9 Months

OCL RAJGANGPUR LINE 2 (RUNNING) 4.2 4700 0.8-2.8 10 Months

DCBL ARIYALUR (RUNNING) 4.35 6000 3.0-6.0 > 1 Year

Name Formula Melting Point (°C)

CaO/SiO2 ratio

<1 > 1 & < 2 >2

Periclase MgO 2840 X X X

MagnesiaFerrite MgFe2O4 1715 X X X

Spinel MgAl204 2135 X X -

Forsterite Mg2SiO4 1890 X - -

MontiCellite CaMgSiO4 1492 X X -

Merwinite Ca3Mg(SiO4)2 1575 - X -

DiCalciumSilicate Ca2SiO4 2130 - X X

TriCalciumSilicate Ca3SiO4 2150 - X X

DiCalciumFerrite Ca2Fe2O5 1449 - - X